1. Field of the Invention
The present invention relates to an image forming apparatus such as a digital copying machine which forms an output image by using digital image data.
2. Description of the Prior Art
An image reader is known to use a scanner moving along a subscan direction to read an image of a document placed on a platen. For example, in an image reader disclosed in U.S. Pat. No. 4,992,350, a document size is detected when a scanner moves along a forward direction and image data is read when the scanner moves along a return direction. Therefore, no prescan for detecting a document size is needed, and if such an image reader is used with a digital copying machine, productivity of copy papers can be improved. It is to be noted that this apparatus reads a document only along one direction. Therefore, discharged copy papers are also put in order along one direction.
A stapler may be attached to a digital copying machine to staple discharged copy papers on which images have been formed. However, the staple position of the stapler on the discharged copy papers is not necessarily located at a position suitable for stapling them. Further, the direction of document images are not necessarily the same. For example, when two-face documents are reproduced, the directions of document images of front and back pages having top margins are reversed to each other. In such a case, the direction of document images are changed alternately. If copy papers including normal and reverse directions of output images are produced, a user has to sort or rearrange them. On the other hand, a digital copying machine is also known to have 2-in-1 mode or 4-in-1 mode where two or four documents are reproduced on a single face of a paper side by side. Then, it is needed that two document or four images on the same face have same document directions even if they are read from a two-face document.